We plan to remove sys_pre_expand in OTP 20:
https://github.com/erlang/otp/pull/1156
sys_pre_expand is an undocumented and unsupported module, but since it
has been in Erlang/OTP since the beginning, we thought it better to
give a heads up just in case.
/Björn
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Björn Gustavsson, Erlang/OTP, Ericsson AB